The CFA/I assembly consists of four functional/structural components: CfaE is a tip-located minor subunit and functions as an adhesive component. CfaB polymerizes into the stalk of a pilus and is therefore named major pilin. CfaA functions as a periplasmic chaperone escorting CfaB or CfaE to their assembly site at the bacterial outer membrane. CfaC, named the usher protein, is an integral outer membrane protein forming the assembly site for the pili. As part of the NIHs Biodefense program, my lab has been working on structure determination of CFA/I of ETEC. We have determined subunit structures of the major pilin (CfaB) and the minor subunit (CfaE). We also obtained structures for their complexes in various forms such as the minor and major pilin complex CfaEB, the complexes between major pilins such as CfaBB and CfaBBB. Based on these structures, we identified the receptor-binding site for the adhesive subunit, which was subsequently confirmed with site-directed mutagenesis and we obtained a putative model for the pilus assembly.